In general, in a power conversion apparatus comprising an inverter, a converter or the like, there are used a plurality of semiconductor devices (GTO, IGBT, etc.) corresponding to individual phases.
The semiconductor devices, which constitute a main circuit for power conversion, can not operate by themselves, so they are driven to operate under the control of a drive unit which is separately provided.
A conventional semiconductor drive unit comprises a drive circuit that is connected to individual semiconductor devices, and a microcomputer control part that controls the drive circuit (see, for example, a first patent document).
The drive circuit and the microcomputer control part each have an O/E conversion section and an E/O conversion section at their one end, and are connected to each other in individual phases through a plurality of optical fibers (communication mediums) that have end connector portions at opposite ends thereof.
Control signals of individual phases created by the microcomputer control part are converted into optical signals and then sent to the drive circuit through the individual optical fibers, and they are further converted into electric signals, which are impressed to the individual semiconductor devices thereby to turn on and off the individual semiconductor devices.
In addition, the drive circuit has a protection detection section that monitors the abnormality of each of the individual semiconductor devices, and inputs a fault signal to a fault processing circuit in the microcomputer control part thereby to stop the apparatus.
For example, in case where the power conversion apparatus is in the form of a three-phase two-level inverter, ON/OFF commands (control signals) for three phases (U phase, V phase and W phase) of an upper arm and three phases (X phase, Y phase and Z phase) of a lower arm have a phase difference of 120 degrees between adjacent phases, and the individual control signals are set in reverse logic with a dead time interposed between adjacent ones in such a manner that the control signals for the upper arm and the lower arm are not turned on at the same time.
At this time, for example, when an optical fiber corresponding to a semiconductor device of the X phase and an optical fiber corresponding to a semiconductor device of the V phase are exchanged or reversed with each other and mis-connected to the optical fibers of the V phase and the X phase, respectively, a semiconductor device of the upper arm and a semiconductor device of the lower arm can be turned on at the same time for each phase for a certain period of time if left as they are, thus giving rise to the possibility that an arm short fault might be caused to damage the semiconductor devices.
First Patent Document    Japanese patent application laid-open No. 2003-143832